This application is cross-related to French patent application No. 0207603, filed Jun. 19, 2002.
This invention relates to high contrast photographic silver halide materials and in particular to materials of the graphic arts type containing a hydrazide nucleating agent.
In the field of graphic arts, an ultrahigh contrast photographic material is required for achieving satisfactory halftone dot reproduction of a continuous tone or reproduction of a line image in the process of making a lithographic printing plate. For many years these ultrahigh contrast photographic images were obtained by developing a xe2x80x98lithxe2x80x99 emulsion (usually high in silver chloride content) in a hydroquinone, low sulfite, xe2x80x98lithxe2x80x99 developer by the process known as infectious development. However, such low sulfite developers are inherently unstable and are particularly inappropriate for machine processing.
More recently an image formation system providing ultrahigh contrast where the gamma (contrast) exceeds 10 has been provided conventionally in a material wherein silver halide bearing a surface latent image is developed in the presence of a hydrazine (also known as a nucleating agent), specifically an acylhydrazine, which can be incorporated into the photographic material or into the developer. The pH of the developer solution is usually in the range 10.0 to 12.3, typically about 11.5, and the developer includes conventional amounts of sulfite, hydroquinone and possibly metol or a pyrazolidone. While such a process is better than the low sulfite xe2x80x98lithxe2x80x99 process, the developer still has a high pH requirement for it to function correctly. Such a solution is not as stable as is desirable. Additionally, high pH solutions are environmentally undesirable because of the care needed in handling and disposing of the effluent.
Unfortunately, light sensitive materials whose contrast is enhanced by the presence of a hydrazine nucleating agent show large variations in their photographic properties as the developer is exhausted or through the course of time, for example as the pH of the developer varies and in particular as the pH is lowered. The pH of the developer can vary for a number of reasons: for example, exhaustion and absorption of carbon dioxide causes the pH to drop whilst air oxidation causes the pH to rise, as can concentration through evaporation.
Also during development of silver halide materials, particularly those which use chlorobromide emulsions, there is a release of bromide locally into area of the development as a consequence of the development process to convert silver halide to elemental silver. Both of these effects can influence the development rate of the film and give rise to process unevenness or variability during the processing run. There is an overall effect which shows up as a change to the developer component levels in solution but there is also a local effect which occurs within the developing layer and is exposure dependent. These effects can also depend on the formulation of the developer used and overcoming these problems can increase tolerance to a wider range of developer formulations.
It is also known that a developer solution having a pH below 11 can be employed by using certain hydrazides active at this pH. Hydrazides proposed for such use are described, for example, in U.S. Pat. Nos. 4,278,748; 4,031,127; 4,030,925; 4,323,643; 4,988,604 and 4,994,365 and in EP-A-0 333 435. A nucleating agent containing both a hydrazide moiety and a nicotinamide moiety is disclosed in U.S. Pat. No. 5,288,590. However the use of such a nucleating agent does not entirely remove sensitivity to both bromide and pH.
A nucleating agent which comprises a dimeric molecule comprising two monomers linked by a linking group, each monomer of which (a) may be the same or different and (b) comprises a hydrazide and a nicotinamide moiety has been disclosed in U.S. Pat. No. 6,228,566. A nucleating agent comprising (a) two nicotinamide moieties, which may be the same or different, which are linked by a linking group, and (b) a hydrazide moiety linked to only one of those nicotinamide moieties, either alone or together with the nucleating agent comprising the dimeric molecule, has been described in U.S. Pat. No. 6,245,480. A nucleating agent as described in either of these two US patents in combination with a xe2x80x98conventionalxe2x80x99 aryl sulfonamido aryl hydrazide is described in EP-A-1 229 383. U.S. Pat. Nos. 4,988,604 and 4,994,365 describe aryl sulfonamidophenyl hydrazide nucleating agents which are capable of high contrast development.
Developer solutions with pHs below 11 can also be used by the introduction of a contrast-promoting agent (commonly called a booster) to give adequate activity. The booster can be incorporated into the photographic layer or may be dissolved in the developer solution. The booster may be, for example, one of the boosters as described in U.S. Pat. No. 5,316,889 or an amine booster as described in U.S. Pat. Nos. 4,269,929; 4,668,605, 4,740,452 or EP-A-0 364 166. Compounds bearing different functionalities e.g. phosphonium and pyridinium, have also been shown to be active, as described in U.S. Pat. No. 5,744,279.
In the non-image areas on the processed film unwanted small dots can appear and this is called xe2x80x98pepper fogxe2x80x99. This is due to unintentionally fogged grains developing and being amplified by the nucleation process and being rendered visible. Nucleating agents which are unstable or more active and diffuse more rapidly can result in more and larger pepper fog spots. In high contrast materials therefore a balance needs to be achieved between vigorous development and pepper fog.
Another factor to be considered is chemical spread (or image spread) which is a measure of the increase in size of developed dots or lines produced by nucleation of the edge of the image area causing development of the image boundary beyond the original exposed edge. This spread is small but measurable and can reduce the resolution of very fine lines.
A further consideration is the efficiency of synthesis of the nucleating agents and the robustness of the chemical processes used in their synthesis. It is desirable that the nucleating agents and their intermediates are formed rapidly and efficiently at all stages of the synthesis since heating and/or prolonged reaction times can have an adverse effect on their purity. Furthermore, whilst it may be desirable from the cost point of view to prepare a mixture of nucleating agents (as in U.S. Pat. No. 6,245,480) without the need for purification or separation of the nucleating agents, for regulatory purposes it is mandatory to provide a mixture wherein the proportions of components are within defined limits. When a chemical reaction produces a mixture of nucleating agents and impurities it is not always possible to ensure that the various components will be within the defined limits and thus the process, although cost effective when successful, is less robust and consistent than desired.
The problem is therefore to provide a nucleating agent, for incorporation into a photographic material or into the developer, which gives ultrahigh contrast whilst at the same time showing less sensitivity to variations in the developing conditions, such as pH or development time, and which may be synthesised rapidly, efficiently, in a cost effective and robust manner and having consistent purity and constitution.
The nucleating agents for use in this invention show unexpectedly good nucleation and less sensitivity to variation in the development conditions than do conventional nucleating agents, leading to significant improvements in processing robustness. A further benefit resides in that the syntheses of the nucleating agents of this invention are more consistent, efficient and robust than those of the dimeric nucleators and mixtures of dimeric nucleating agents previously reported in the literature.
It has now been found that the objectives of the invention can be achieved by the use of a nucleating agent comprising 2 to 4 hydrazide moieties wherein the hydrazide moieties are linked directly to one another or to one another by a linking group.
According to the present invention therefore there is provided an ultrahigh contrast photographic material comprising a support bearing a silver halide emulsion layer, containing at least one hydrazide nucleating agent in the emulsion layer and/or a hydrophilic colloid layer, characterised in that the nucleating agent has the formula (I): 
wherein
each A1 and each A2 is independently selected from the class consisting of a hydrogen atom, an unsubstituted or substituted acyl group and an alkyl- or aryl-sulfonyl group;
each Y is independently selected from the class consisting of an unsubstituted or substituted aryl or heterocyclic ring or ring system;
each X is independently selected from the class consisting of Sxe2x95x90O, C, Cxe2x80x94NH and Cxe2x80x94O;
each Lxe2x80x2 is independently selected from the class consisting of an unsubstituted or substituted alkylene group and an unsubstituted or substituted aryl or heterocyclic ring or ring system, linked to Z via an unsubstituted or substituted alkylene group, either directly or via a group selected from the class consisting of NR1COxe2x80x94, NR1CONR2xe2x80x94, OCONR1xe2x80x94 or NR1COOxe2x80x94, wherein R1 and R2 are independently selected from the class consisting of a hydrogen atom and an unsubstituted or substituted alkyl group;
each Z is independently selected from an unsubstituted or substituted group, ring or ring system attached via a heteroatom selected from the class consisting of sulfur, nitrogen, oxygen or phosphorus;
each L is independently a divalent, trivalent or tetravalent linking group;
p and each n are independently 0 or 1
k is an integer from 0 to 8;
and m is an integer from 2 to 4 provided that
when p is 0, n is 0 and m is 2;
when p is 1, n is 0 or 1 and m is 2, 3 or 4; and
T is a counterion or a salt forming acid.
In another aspect of the invention there is provided an ultrahigh contrast photographic material, as hereinbefore defined, which also contains in the emulsion layer or a hydrophilic colloid layer, a booster compound, as hereinafter defined.
In yet another aspect of the invention there is provided a process of forming a photographic image having ultrahigh contrast which comprises imagewise exposing a photographic material comprising a support bearing a silver halide emulsion layer and processing it with an alkaline developer solution, characterised in that it is developed in the presence of a nucleating agent of formula (I), optionally in the presence of a booster compound, as hereinafter defined
The nucleating agents in accordance with this invention have the general structure as described in the Summary of the Invention.
In formula (I), each A1 and each A2 is independently hydrogen or an unsubstituted or substituted acyl group, such as, for example a trifluoroacetyl group, or an unsubstituted or substituted alkyl- or aryl-sulfonyl group, but preferably each A1 and each A2 is a hydrogen atom.
Each Y is independently an unsubstituted or substituted aryl ring or ring system, such as, for example, a phenyl or naphthyl group, or an unsubstituted or substituted heterocyclic ring or ring system, such as, for example, a pyridine, pyrrole, furan, thiophene, thiazole, imidazole, or a benzo derivative of any of these. However each Y is preferably a phenyl group, optionally substituted, for example, with from 1 to 4 substituents selected from halogen, hydroxy, cyano and an unsubstituted or substituted alkyl, aryl, heterocyclyl, alkoxy, acyloxy, aryloxy, carbonamido, sulfonamido, ureido, thioureido, semicarbazido, thiosemicarbazido, urethane, quatemary ammonium, alkyl- or aryl-thio, alkyl- or aryl-sulfonyl, alkyl- or aryl-sulfinyl, carboxyl, alkoxy- or aryloxy-carbonyl, carbamoyl, sulfamoyl, phosphonamido, diacylamino, imido or acylurea group, a group containing a selenium or a tellurium atom, and a group having a tertiary sulfonium structure.
More preferably each Y is an unsubstituted phenyl group or a phenyl group substituted, for example, with an alkylthio or alkylsulfonamido group or in particular with an alkyl or alkoxy group, especially in a position ortho to the hydrazino group, or with, for example, a trifluoromethyl group, especially in a position meta to the hydrazino group.
Each X is independently selected from Sxe2x95x90O, C, Cxe2x80x94NH and Cxe2x80x94O but is preferably Sxe2x95x90O or C. When X is Sxe2x95x90O, Cxe2x80x94NH or Cxe2x80x94O, Lxe2x80x2 can comprise an unsubstituted or substituted alkylene group, especially a methylene group, but it is preferred that Lxe2x80x2 comprises an unsubstituted or substituted aryl ring, preferably a phenyl ring, linked to Z via an unsubstituted or substituted alkylene group, especially a methylene group, either directly or preferably via a NR1CO-group, wherein R1 is a hydrogen atom or an unsubstituted or substituted alkyl group, more particularly via a NHCO-group. The aryl ring of Lxe2x80x2 may suitably be substituted, for example, with one or more alkyl, carboxyl or halogen atoms, and in particular with one or more trifluoromethyl or alkyl groups. When X is C it is preferred that Lxe2x80x2 comprises an unsubstituted or substituted alkylene group, preferably a methylene group.
Each Z is independently an unsubstituted or substituted group, ring or ring system attached via a heteroatom selected from sulfur, nitrogen, oxygen or phosphorus and may be or form with the heteroatom, for example, an alkyl group or a heterocyclic ring, such as a pyridyl or imidazolyl ring, or an alkyl-, aryl- or heterocyclyl- thio group, such as for example, a mercaptopropionic acid, mercaptopyridyl or mercaptotetrazole group or an amino, quatemary ammonium, phosphine, phosphonium, sulfonium, thioureido, isothiouronium or thiocarbamate group. Suitable substituents include, for example, an alkyl, aryl, alkylamino, dialkylamino, cyclohexenyl, piperidinyl, pyridyl, carbonamido, alkylcarbonamido or dialkylcarbonamido group, any of which may be further substituted, for example with one or more alkyl, hydroxy, pyridylcarbonamido or alkynyl groups.
More preferably Z is attached via a nitrogen or a sulfur atom and is most preferably an unsubstituted pyridyl group or a pyridyl group substituted, for example, with an alkyl, dialkylamino, cyclohexenyl, piperidinyl, pyridyl, carbonamido or alkylcarbonamido group, or Z is a thioureido, mercaptopyridyl, thiocarbamate or mercaptotetrazole, substituted, for example, with an alkyl or aryl group, any of the above groups of which may in turn be further substituted.
Each linking group L, when present, is independently selected from a divalent, trivalent or tetravalent group, such as an unsubstituted or substituted aromatic, alkylene, polyalkylene or polyalkylene oxide group or an unsubstituted or substituted alkylene or polyalkylene group separated by one or more heteroatoms selected from nitrogen, oxygen and sulfur, wherein the groups within L may also be separated from each other by one or more unsubstituted or substituted alkyl, alkylene, polyalkylene, aryl or heterocyclic groups, such as a piperidino group. Each linking group L may include, linked to each carbonyl group, a terminal oxygen atom or a group NRxe2x80x2, wherein Rxe2x80x2 is a hydrogen atom or an unsubstituted or substituted alkyl group. Preferred linking groups are, for example, the groups xe2x80x94NH(CH2)2NHxe2x80x94, xe2x80x94NH(CH2)6NHxe2x80x94, xe2x80x94(CF2)2xe2x80x94, xe2x80x94(CF2)3 xe2x80x94, xe2x80x94NH(CH2)2O(CH2)2O(CH2)2O(CH2)2NHxe2x80x94, xe2x80x94OC6H4C(CH3)2C6H4Oxe2x80x94 and in particular the group xe2x80x94NH(CH2)n- piperidino-(CH2)nNHxe2x80x94, wherein n is 0 to 4 and especially 3.
The anionic counterion may be selected from any well-known in the art and may typically be selected from Clxe2x88x92, Brxe2x88x92, CF3CO2xe2x88x92, CH3SO3xe2x88x92and TsOxe2x88x92or their corresponding acids HCl, HBr, CF3CO2H, CH3SO3H and TsOH. k is an integer from 0 to 8, preferably from 0 to 4.
When p and each n are 0, then m is 2 and the compound of formula (I) is of the oxalyl-type, typified by nucleator I-29. When p is 1, i.e. there is a linking group between the carbonyl groups, and each n is independently 0 or 1, then m is either 2, 3 or 4 and is typified by nucleator I-1.
Although for ease of synthesis it may be convenient for the nucleator to be symmetrical, asymmetrical nucleating agent structures are specifically within the scope of this invention.
As used herein and throughout the specification unless where specifically stated otherwise, the term xe2x80x9calkylxe2x80x9d refers to a saturated or unsaturated, straight or branched chain alkyl group including alkenyl and aralkyl, and includes cyclic groups, including cycloalkenyl, having 3-8 carbon atoms. The term xe2x80x9cpolyalkylenexe2x80x9d refers to an alkylene group (CH2)n wherein n is more than 10 and the term xe2x80x9carylxe2x80x9d includes fused aryl.
Unless otherwise specifically stated, substituent groups which may be substituted on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for photographic utility. When the term xe2x80x9cgroupxe2x80x9d is applied to the identification of a substituent containing a substitutable hydrogen, it is intended to encompass not only the substituent""s unsubstituted form, but also its form further substituted with any group or groups as herein mentioned. Suitably, the group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous or sulfur. The substituent may be, for example, halogen, such as chlorine, bromine or fluorine; nitro; hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy and 2-dodecyl-oxyethoxy; aryl such as phenyl, 4-t-butyl-phenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido, alpha-(2,4-di-t-pentylphenoxy)acetamido, alpha-(2,4-di-t-pentyl-phenoxy)butyramido, alpha-(3-pentadecylphenoxy)hexanamido, alpha- (4-hydroxy-3-t-butylphenoxy)tetradecanamido, 2-oxopyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl and N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxy-carbonylamino, phenylcarbonylamino, 2,5-(di-t-pentylphenyl)carbonylamino, p-dodecylphenylcarbonyl amino, p-toluylcarbonyl amino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-dioctyl-Nxe2x80x2-ethylureido, N-phenylureido, N,N-di-phenylureido, N-phenyl-N-p-toluylureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-t-pentylphenyl)-Nxe2x80x2-ethylureido and t-butylcarbonamido; sulfonamido, such as methylsulfonamido, benzenesulfonamido, p-toluylsulfonamido, p-dodecylbenzenesulfonamido, N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino and hexadecylsulfonamido; sulfamoyl, such as N-methyl-sulfamoyl, N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl; N-[3-(dodecyloxy)propyl]sulfamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl, N-methyl-N-tetradecylsulfamoyl and N-dodecylsulfamoyl; carbamoyl, such as N-methylcarbamoyl, N,N-dibutyl-carbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]-carbamoyl, N-methyl-N-tetradecylcarbamoyl and N,N-di-octylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl, p-dodecyloxy-phenoxycarbonyl, methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl and dodecyl-oxycarbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyl-oxysulfonyl, 2-ethylhexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentyl-phenoxysulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl and p-toluylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy and hexadecyl-sulfonyloxy; sulfinyl, such as methylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl and p-toluylsulfinyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-t-pentylphenoxy)-ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio and p-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy and cyclohexylcarbonyloxy; amino, such as phenylanilino, 2-chloroanilino, diethylamino and dodecylamino; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzyl-hydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3 to 7 membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of oxygen, nitrogen and sulfur, such as 2-furyl, 2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such as triethylammonium; and silyloxy, such as trimethylsilyloxy.
If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain the desired photographic properties for a specific application and can include, for example, hydrophobic groups, solubilizing groups, blocking groups, releasing or releasable groups. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.
Specific examples of nucleators falling under the scope of the invention are shown below: 
The photographic material of the invention may also contain a booster compound to enhance the ultrahigh contrast and to promote activity. Alternatively the booster compound can be present in the developer solution.
One class of such boosters are amines which
(1) comprise at least one secondary or tertiary amino group, and
(2) have an n-octanol/water partition coefficient (log P) of at least one, preferably at least three, and most preferably at least four,
log P being defined by the formula:       log    ⁢          xe2x80x83        ⁢    P    =      log    ⁢                  [                  X          octanol                ]                    [                  X          water                ]            
wherein
X is the concentration of the amino compound.
Preferably such an amine contains within its structure a group comprising at least three repeating ethyleneoxy units as described in U.S. Pat. No. 4,975,354. These units are preferably directly attached to the nitrogen atom of a tertiary amino group.
Included within the scope of the amino compounds which may be utilised in this invention are monoamines, diamines and polyamines. The amines can be aliphatic amines or they can include aromatic or heterocyclic moieties. Aliphatic, aromatic and heterocyclic groups present in the amines can be substituted or unsubstituted groups. Preferably, the amine boosters are compounds having at least 20 carbon atoms.
Preferred amino compounds for inclusion in photographic materials of the invention are bis-tertiary-amines which have a partition coefficient of at least three and a structure represented by the formula:
R1R2Nxe2x80x94(CH2CH2O)nxe2x80x94CH2xe2x80x94CH2xe2x80x94NR3R4
wherein
n is an integer from 3 to 50, and more preferably 10 to 50;
R1, R2, R3 and R4 are, independently, alkyl groups of 1 to 8 carbon atoms, or
R1 and R2 taken together represent the atoms necessary to complete a heterocyclic ring, and/or R3 and R4 taken together represent the atoms necessary to complete a heterocyclic ring.
A particularly preferred booster for use in photographic materials of the invention or in the developer therefor is the booster B1 wherein in the above formula R1, R2, R3 and R4 are each n-propyl groups and n is 14, i.e. the structure 
Another preferred group of amino compounds are bis-secondary amines which have a partition coefficient of at least three and a structure represented by the formula: 
wherein
n is an integer from 3 to 50, and more preferably 10 to 50, and each R is, independently, a linear or branched, substituted or unsubstituted, alkyl group of at least 4 carbon atoms.
Particular amines suitable as booster compounds are listed in EP-A-0 364 166.
Other types of boosters are described in U.S. Pat. No. 5,744,279 as having one of the formulae:
Y((X)n-A-B)mxe2x80x83xe2x80x83(a)
wherein
Y is a group which adsorbs to silver halide,
X is a divalent linking group composed of hydrogen, carbon, nitrogen and sulphur atoms,
A is a divalent linking group,
B is an amino group which may be substituted or an ammonium group of a nitrogen-containing heterocyclic group,
m is 1, 2 or 3 and
n is 0 or 1,
R1R2N-R3-(X)n-SMxxe2x80x83xe2x80x83(b)
wherein
R1 and R2 are each hydrogen or an aliphatic group, or
R1 and R2 may together form a ring,
R3 is a divalent aliphatic group,
X is a divalent heterocyclic ring having at least one nitrogen, oxygen or sulphur atom as heteroatom,
n is 0 or 1,
Mx is hydrogen or an alkali metal atom, alkaline earth metal atom, a quaternary ammonium, quaternary phosphonium atom or an amidino group; said compound optionally being in the form of an addition salt;
(c) a phosphonium structure as disclosed in U.S. Pat. No. 5,744,279 and as exemplified by the following formula: 
or
(d) a pyridinium structure as disclosed in U.S. Pat. No. 5,744,279 as exemplified by the following formula: 
The nucleating agent and optionally the booster compound can be incorporated in the photographic element, for example it can be incorporated in a silver halide emulsion layer. Alternatively it can be present in a hydrophilic colloid layer of the photographic element, preferably a hydrophilic layer which is coated to be adjacent to the emulsion layer in which the effects of the nucleating agent are desired. It can however be present in the photographic element distributed between or among emulsion and hydrophilic colloid layers, such as undercoating layers, interlayers and overcoating layers.
Typically the nucleating agent may be present in the photographic material in an amount of from about 1 xcexcmol/m2 to about 100 xcexcmol/m2, preferably 3 xcexcmol/m2 to 50 xcexcmol/m2, more preferably 5 xcexcmol/m2 to 20 xcexcmol/m2. Corresponding amounts for the booster are from 0 mol/m2 to about 1 xcexcmol/m2, preferably 10 xcexcmol/m2 to 100 xcexcmol/m2, most preferably 30 xcexcmol/m2 to 100 xcexcmol/m2.
The emulsions employed in photographic materials of the invention and the addenda added thereto, the binders, supports etc. may be as described in Research Disclosure Item 36544, September 1994, published by Kenneth Mason Publications, Emsworth, Hants, PO10 7DQ, United Kingdom, which will be identified hereinafter by the term xe2x80x9cResearch Disclosure.xe2x80x9d
The hydrophilic colloid may be gelatin or a gelatin derivative, polyvinylpyrrolidone or casein and may contain a polymer. Suitable hydrophilic colloids and vinyl polymers and copolymers are described in Section IX of the Research Disclosure. Gelatin is the preferred hydrophilic colloid. The photographic materials may also contain an overcoat hydrophilic colloid layer which may also contain a vinyl polymer or copolymer located as the last layer of the coating (furthest from the support). It may contain one or more surfactants to aid coatability and may contain some form of matting agent. The vinyl polymer is preferably an acrylic polymer, preferably containing units derived from one or more alkyl or substituted alkyl acrylates or methacrylates, alkyl or substituted alkyl acrylamides, or acrylates or acrylamides containing a sulfonic acid group.
The photographic materials of the invention preferably contain an antihalation layer which may be on either side of the support, preferably on the opposite side of the support from the emulsion layer. In a preferred embodiment an antihalation dye is contained in the hydrophilic colloid underlayer. The dye may also be dissolved in or dispersed in the underlayer. Suitable dyes are listed in the Research Disclosure disclosed above.
The emulsions are preferably chemically sensitised, for example with both sulfur and gold. The latent-image forming grains can be bromoiodide, chlorobromoiodide, bromide, chlorobromide, chloroiodide or chloride, preferably chlorobromide. They should be preferably be spectrally sensitised. More than one type of spectrally sensitised silver halide grain may be present and hence grains sensitised to different spectral regions may be present in the emulsion layer.
The coating may be made by blending two or more emulsion melts containing grains of the required spectral sensitivity, allowing the production of multi-wavelength sensitive products and giving rise to manufacturing cost advantages through both material and inventory reduction. Combining the different emulsion grains within one layer can give improvements in process sensitivity over multi-layer graphics nucleated systems, as described in EP-A-0 682 288.
The silver halide grains may be doped with rhodium, ruthenium, iridium or other Group VIII metals either alone or in combination, preferably at levels in the range 10xe2x88x929 to 10xe2x88x923, preferably 106 to 10xe2x88x923 mol metal per mole of silver. The grains may be mono- or poly-disperse. The preferred Group VIII metals are rhodium and/or iridium and ammonium pentachlororhodate may conveniently be used.
The present photographic materials are particularly suitable for exposure by red or infra-red laser diodes, light-emitting diodes or gas lasers, e.g. a Helium/Neon or Argon laser.
The light-sensitive silver halide contained in the photographic elements can be processed following exposure to form a visible image by associating the silver halide with an aqueous alkaline medium in the presence of a developing agent contained in the medium or the element. The photographic elements of this invention can be processed in conventional developers as opposed to specialised developers sometimes employed in conjunction with lithographic photographic elements to obtain very high contrast images. When the photographic elements contain incorporated developing agents the elements can be processed in the presence of an activator, which can be identical to the developer in composition, but otherwise lacking a developing agent. Very high contrast images can be obtained at pH values below 11, preferably in the range of from 10.0 to 10.8, preferably in the range of 10.3 to 10.5 and especially at pH 10.4.
The developers are typically aqueous solutions, although organic solvents, such as diethylene glycol, can also be included to facilitate the solution of organic components. The developers contain one or a combination of conventional developing agents, such as, for example, a polyhydroxybenzene, such as hydroquinone, aminophenol, paraphenylenediamine, pyrazolidone, pyrazolone, pyrimidine, dithionite or hydroxylamine; or ascorbic acid or a related compound thereof, such as sodium erythorbate, which may be in combination with specific para-aminophenols as described in EP-A-793 140.
It is preferred to employ hydroquinone and 3-pyrazolidone developing agents in combination. The pH of the developers can be adjusted with alkali metal hydroxides and carbonates, borax and other basic salts. It is, as previously mentioned, a particular advantage of the present invention that the use of a nucleating agent as described herein reduces the sensitivity of the photographic material to changes in this developer pH.
To reduce gelatin swelling during development, compounds such as sodium sulfate can be incorporated into the developer. Chelating and sequestering agents, such as ethylenediaminetetraacetic acid or its sodium salt, can be present. Generally any conventional developer can be used in the practice of this invention. Specific illustrative photographic developers are disclosed in the Handbook of Chemistry and Physics, 36th Edition, under the title xe2x80x9cPhotographic Formulaexe2x80x9d at page 30001 et seq. and in xe2x80x9cProcessing Chemicals and Formulas.xe2x80x9d 6th Edition, published by Eastman Kodak Company (1963).
The invention will now be described with reference to the following examples which are in no way to be considered as limiting the scope thereof.